Cementitious building materials such as concrete are used in large volumes throughout the world. By varying the proportions of ingredients used in the cementitious premix, many types of concrete are available. These include floor levelling and repair products. Such products are used, for example, in preparing a floor prior to the laying of a covering such as carpet or vinyl. These products are designed to find their own levels when installed at a thickness of 3 mm or greater. Once hydrated and poured the cementitious mix hardens and sets rapidly so that it can be walked on within as little as two to three hours. It is often desired to improve the aesthetic qualities of building materials by introducing colour. To achieve this the surface of the building material may be either dyed or colour added during the forming of the material (referred to here as “integral colouring”).
As discussed in the publication of Hertz et al (2012) several methods for dyeing a concrete surface are known. A first method involves washing the surface with an acidic solution containing a metal salt. Following development of the colour a neutralising agent, then a clear protective polymeric sealing coating are applied. A second method involves washing the surface with an acidic solution to roughen or etch the surface before colouring the surface with a polymer based stain or paint and finishing with a clear coating. A third method involves etching or grinding the surface before applying a cementitious overlay. The cementitious overlay is then stained with an acidic solution containing a metal salt. These methods are generally disadvantageous due to the use of highly corrosive acidic solutions which are hazardous to handle.
Historically, the integral colouring of concrete has been achieved by adding formulations of inorganic pigments such as iron oxide to the hydrated premix. A range of earth tones are thereby obtainable. Ingredients used in the cementitious premix, such as those added to provide integral colour or the requisite “self-levelling” properties of floor levelling and repair products, must not adversely affect the durability and strength of the building material once formed. Furthermore, ingredients added to a cementitious premix to provide colour should not interfere with the function of additives included, for example, to provide “self-levelling” properties. By way of illustration, inorganic pigments such as iron oxide can inhibit the performance of shrinkage-compensating additives used in floor levelling and repair products resulting in cracking. Many different formulations of pigments have been proposed for integral colouring of cementitious building materials, especially concrete.
The publication of Tomkinson (1971) discloses colouring materials deposited on iron oxide particles obtained by precipitation. Preferred colouring materials include carbon black, azo colouring materials, vat dyes (anthraquinoid and indigoid) and phthalocyanine colouring materials. The pigments thereby provided are proposed for use in colouring concrete, tile and brick.
The publication of Bowen (1980) states that it is difficult to obtain a sufficiently thorough mixing of powders into a wet cement mix so as to achieve a homogenous colour throughout the mixture. The publication discloses stabilized thixotropic slurries for colouring concrete comprising pigment, at least one stabilizer, a dispersant and water.
The publication of Jungk (1990) discloses granules for use in colouring concrete consisting of one or more pigments and one or more binders for promoting the dispersing of the pigments in the concrete. Ammonium lignin sulfonated powder is used as the binder.
The publication of Kröckert and Linde (1993) discloses a process for colouring building materials. The process uses inorganic pigments (iron oxides, titanium oxide) formulated as granules. The granules are prepared by spray-drying aqueous suspensions of 38 to 55% by weight of the inorganic pigments and 0.3 to 1.3% by weight of soluble salts. The granules are asserted to have at least satisfactory flow behaviour and rapid dispersibility in concrete.
The publication of Linde and Eitel (1996) discloses a process for the colouration of building materials such as concrete by granulated inorganic pigments. The commercially available formulations of inorganic pigments (Bayer AG) are mixed with a small amount of machine or vegetable oil, compacted and then granulated to provide material with a grain size of 0.2 to 2 mm.
The publication of Köhler et al (1998) discloses a process for the preparation of iron oxide black pigment granules which are stable to handling. The process includes a step of tempering spray-dried granules of iron oxide black pigment in an indirectly heated rotary kiln at temperatures below 65° C. in an inert nitrogen atmosphere for approximately 30 to 60 minutes. The granules are asserted to have high strength, dispersibility and stability to oxidation.
The publication of Will (1998) discusses how many inorganic pigments, such as metal oxides, do not disperse well in cementitious systems. The publication discloses a method for colouring cementitious systems using compacted inorganic granules. The compacted inorganic granules comprise an inorganic pigment and a dispersing agent.
The publication of Johansen et al (1999) discloses an aqueous composition for colouring cement-based composition comprising water, pigment, a suspension enhancing agent and latex polymer solids. A mixture of predetermined amounts of a cement-based component and the aqueous composition is asserted to provide a cement-based composition of uniform and standardised colour that is capable of being consistently reproduced.
The publication of Supplee (2003) discloses a composition for colouring concrete. In addition to the colourant the composition includes a stearic acid, salt or derivative as a hydrophobic efflorescence control agent. The composition also includes particulated polymers and co-polymers. The composition is asserted to improve durability of the coloured concrete.
The publication of Dunnous and Yocum (2004) discloses pigment-containing granules for use in colouring concrete. The publication states that forming granules with a soluble organic binder by spray-drying can be problematic due to the high temperature air flow used. It is asserted that if charring of the soluble organic binder occurs it will no longer be readily soluble in water. This technical problem is avoided in the method disclosed by using an insoluble, pozzolanic clay (aluminium silicate) agglomerator.
The publication of Noack and Herrmann (2004) discloses colouring pigment granulates. The granulates comprise granulated cores that do not contain binders, emulsifying agents, surface active agents, dispersing agents, or preservatives. The granulates cores are enclosed by an enveloping layer made of a material such as polyvinyl alcohol, that can be broken down. The absence of binders and other auxiliaries is asserted to ensure rapid disagglomeration once the shell enveloping material is broken down.
The publication of Supplee (2007) discloses compositions for colouring concrete when integrally or surface-shake applied. The composition comprises a spray-dried styrene acrylic polymer encapsulated colourant and a second polymer for use in dispersing the encapsulated colourant.
The standard of Anon (2010) prescribes that coloured concrete pigmented at a maximum dosage rate of 10% by weight of the cement shall have a 28-day compressive strength of not less than 90% and a water to cement ratio of not greater than 110% of that of the control. The standard further prescribes that when added to concrete at the maximum dosage rate, the pigment is to neither accelerate the initial or final set by more than one hour nor retard the initial or final set by more than one and a half hours, and the air content is not be changed by more than 1% as compared to the control.
It is an object of the invention to provide a method of colouring concrete capable of complying with the requirements of the standard of Anon (2010). It is an object of the invention to provide colourants for use in the method. These objects are to be read disjunctively with the object to provide at least a useful choice in the colouring of cementitious building materials.